The present invention pertains to thermosettable prepolymers prepared from heterocyclic materials having alkyl substituents, mono- or dianhydrides, polymerizable ethylenically unsaturated materials and an aqueous or alcoholic solution of a hydroxide, carbonate or bicarbonate of a metal of Groups I-A or II-A. These prepolymers when cured provide products which have good char formation when subjected to 700.degree. C. in air.
Prepolymers disclosed in a copending application Ser. No. 754,695, filed on July 15, 1985, now U.S. Pat. No. 4,752,636, prepared from (1) a heterocyclic material having at least one ring and at least one nitrogen atom therein and at least two reactive alkyl substituent groups (2) a cycloaliphatic or aromatic carboxylic acid mono- or dianhydride and (3) a compound containing both a polymerizable ethylenically unsaturated group and at least one group selected from (a) a heterocyclic material having one or more rings and at least one nitrogen atom in a ring and at least one substituent group which as at least one reactive alkyl group which has a reactive hydrogen atom or (b) a cycloaliphatic or aromatic carboxylic acid mono- or dianhydride exhibit, when cured, a char yield of about 64-66 weight percent when subjected to a temperature of about 950.degree. C. in nitrogen. Unfortunately, these cured polymers exhibit a zero percent char yield at 700.degree. C. in air.
It has been discovered that when these prepolymers are reacted with an aqueous or alcoholic solution of a hydroxide, carbonate or bicarbonate of a metal of Groups I-A or II-A, the resultant cured product exhibits an improved char yield when subjected to a temperature of 700.degree. C. in air.